Iron is an essential trace element in animal and human nutrition. It is a component of heme in hemoglobin and of myoglobin, cytochromes and several enzymes. The main role of iron is its participation in the transport, storage and utilization of oxygen. A balanced diet will normally cover the need of iron through intake of iron rich food stuff such as vegetables, meat and cereals. An important iron source is cereals such as wheat flour. However in modern methods of producing wheat flour the iron rich shell of the wheat grain is eliminated. This results in that the iron content of wheat flour of today is lower than that of wheat flour produced before. Iron deficiency is also a consequence of the malnutrition which is pre-vailing especially in the developing countries. As a diet with too low iron content contributes to low birth weights impairs growth and cognitive development in children and causes fatigue among adults there is a need of adding iron to the diet. The greatest effect of an iron fortification program will of course be reached when iron is added to food that most people eat daily.
The most widespread method is iron fortification of cereal products such as wheat flour, corn flour, corn flakes etc. but many other products are also fortified.
Iron can be added to food and feed in many different forms. Metallic iron can be used as well as inorganic salts of iron, such as iron sulphate, and organic salts, such as iron gluconate or iron fumarate. There are basically three different types of elemental iron for food fortification, namely reduced iron or sponge iron, carbonyl iron and electrolytic iron.
The reduced iron is produced by a reduction of ground iron oxide with hydrogen or carbon monoxide at elevated temperature followed by grinding and milling of the reduced iron cake. Reduced iron is produced from either iron ore or mill scale. The purity of the product is dictated by the purity of the iron oxide. These products have the lowest purity of the food grade iron powders when compared with-electrolytic or carbonyl powders. The most common impurity in iron powder produced by any reduction process is oxygen, most of which occurs as a thin film of surface oxide. Basic impurities include carbon, magnesium, aluminium, silicon, phosphorus, sulphur, chromium, manganese, nickel and copper, many of which are present as oxides. The particle size is irregular and porous and it consists of a number of small equiaxed grains.
Carbonyl iron powders consist of particles, which are much finer than particles of other iron powders. These powders are produced by treating reduced iron with carbon monoxide under heat and pressure. The resulting iron pentacarbonyl is later decomposed under controlled conditions yielding an iron powder and carbon monoxide gas. At this point the major impurity is carbon and further reduction in wet hydrogen is necessary to remove most of the carbon. The powder has particles ranging in size from 0.5 to 10 μm in diameter and is of high purity. The particles are close to spherical in shape and very dense and smooth. The structure of the particles is characterized by concentric shells arranged in onion-skin fashion. The carbonyl process is costly.
Electrolytic iron is produced by electrolytic deposition of a hard brittle metal that is mechanically comminuted. The particle shape of electrolytic iron powder is irregular, dendritic of fernlike, from which it receives its high surface factor.
An important feature for the iron containing compounds used as food additive is the bioavailability of the iron i.e. how efficiently the iron is absorbed by the body. Of the iron powders used for food and feed enrichment today, the carbonyl and electrolytic powders have the highest bioavailability but the production costs of these powders are high compared with the production costs for reduced iron powders. A pure reduced iron powder, which has high bioavailability and which can be cost effectively produced would therefore be attractive and is the object of the present invention.
The assessment of bioavailability may be performed in different ways such as in vitro studies, animal studies or human studies. Bioavailability of iron powders as well as other iron compounds are usually measured relative to iron sulphate.